JP2009260000A - Manufacturing method of laminated ceramic capacitor - Google Patents

Abstract

An object of the present invention is to provide a method for manufacturing a multilayer ceramic capacitor capable of reducing the influence of the amount of ZrO ₂ mixed in a dielectric green sheet and obtaining a target capacitance.
A method of manufacturing a multilayer ceramic capacitor that is fired by changing the oxygen concentration of the atmosphere during firing according to the amount of ZrO ₂ contained in the dielectric green sheet, and thereby mixed into the dielectric green sheet. The influence of the amount of ZrO ₂ can be reduced to reduce the variation of the dielectric constant of the dielectric layer, and the target capacitance can be obtained without changing the thickness of the dielectric, the number of stacked layers, the internal electrode area, etc. Can do.
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Description

  The present invention relates to a method for producing a multilayer ceramic capacitor used in various electronic devices.

  In recent years, multilayer ceramic capacitors have been rapidly reduced in size and capacity, and in order to realize them, a method of thinning dielectric layers per layer in the multilayer ceramic capacitor has been taken. In order to reduce the cost, the internal electrode is generally made of nickel instead of the former noble metal such as Pd. As the thickness of the dielectric layer is reduced, the structure of one dielectric layer greatly affects the characteristics of the capacitor. Therefore, homogenization of the characteristics of the dielectric layer has become extremely important.

  For example, as disclosed in Patent Document 1, the multilayer ceramic capacitor is manufactured by the following manufacturing method.

  After alternately laminating multiple layers of dielectric green sheets as dielectric layers and paste films consisting mainly of nickel powder as internal electrodes, cut them into individual laminates, which are placed in a nickel reducing atmosphere. After firing into a sintered body, external electrodes are formed on the sintered body to produce a multilayer ceramic capacitor.

  Moreover, the dielectric green sheet is produced as follows, for example. First, barium titanate, which is the main ingredient of the raw material powder, and auxiliary raw material powders such as manganese oxide and rare earth element oxide are weighed in a predetermined ratio, and these are zirconia balls using water as a solvent. Together with a ball mill and drying to obtain a raw material mixed powder. If necessary, the mixed powder is subjected to a heat treatment such as calcining, and then the calcined powder is mixed with zirconia balls and pure water. After being wet pulverized in a ball mill, it is dehydrated and dried to obtain a dielectric powder. An organic binder, a solvent, and the like are added to the dielectric powder and mixed with a zirconia ball by a ball mill to prepare a slurry, and the slurry is applied and dried by a doctor blade method or the like to produce a dielectric green sheet.

As described above, particularly in recent years, a very thin dielectric green sheet has been produced and used for the purpose of thinning the dielectric layer. Along with the thinning of the dielectric green sheet, the dielectric powder in the dielectric green sheet is homogenized, that is, the mixed dispersion state of the subcomponent metal oxide powder to the main component barium titanate powder is uniform. This is becoming extremely important. In addition, in order to obtain a uniform mixed dispersion state, it is indispensable to highly disperse the dielectric powder in the above-mentioned mixing process when preparing the dielectric powder, the pulverizing process of the calcined powder, and the mixing process when preparing the ceramic slurry. For this reason, it is necessary to process for a long time in each process.
JP-A-10-162648

However, as described above, when a zirconia ball is used as a medium and a ball mill is used for a long time, the ZrO ₂ component of the zirconia ball is mixed in the dielectric green sheet in a large amount as an impurity, and the amount thereof varies. Due to the variation in the amount of ZrO ₂ mixed, the composition of the dielectric powder in the dielectric green sheet varies, and the electrical characteristics such as the dielectric constant of the dielectric layer after sintering vary, resulting in desired electrical characteristics, In particular, there is a problem that a multilayer ceramic capacitor having a desired capacitance cannot be obtained.

The present invention solves the above-described problems, and provides a method for manufacturing a multilayer ceramic capacitor capable of obtaining a target capacitance while reducing the influence of the amount of ZrO ₂ mixed in a dielectric green sheet. It is intended.

In order to achieve the above object, the method for producing a multilayer ceramic capacitor according to the present invention is configured such that firing is performed by changing the oxygen concentration of the atmosphere during firing according to the amount of ZrO ₂ contained in the dielectric green sheet. .

According to the method for manufacturing a multilayer ceramic capacitor of the present invention, the above-described configuration can reduce the influence of the amount of ZrO ₂ mixed in the dielectric green sheet and reduce the variation in the dielectric constant of the dielectric layer. The target capacitance can be obtained without changing the thickness of the dielectric, the number of stacked layers, the internal electrode area, and the like. Moreover, there is no occurrence of internal structural defects such as delamination and cracks in the sintered body, and a highly reliable multilayer ceramic capacitor can be manufactured.

(Embodiment)
Hereinafter, the manufacturing method of the multilayer ceramic capacitor of this invention is demonstrated in detail using one embodiment.

First, barium titanate as a main component and Mn ₃ O ₄ , Al ₂ O ₃ , SiO ₂ , Mg (OH) ₂ , and Dy ₂ O ₃ as subcomponents are weighed to have a predetermined composition, and these weighed raw materials The powder was placed in a ball mill together with zirconia balls and pure water, wet mixed, and then dehydrated and dried. Next, this dry powder was put into a high-purity alumina crucible and calcined at 900 ° C. for 2 hours in air. Thereafter, the calcined powder was placed in a ball mill together with zirconia balls and pure water, wet-pulverized, and then dehydrated to produce a dielectric powder.

  Next, n-butyl acetate as an organic solvent, polyvinyl butyral resin as an organic binder, and BBP (butylbenzyl phthalate) as a plasticizer are added to the above dielectric powder, and mixed with a zirconia ball in a ball mill to produce a ceramic slurry. did. This ceramic slurry was applied and dried on a polyethylene terephthalate film by a doctor blade method to produce a dielectric green sheet having a thickness of 2 μm.

In the production of the dielectric green sheet, the amount of mixed zirconia (ZrO ₂ ) is changed by changing the mixing time of the raw material powder during the dielectric powder production, the grinding time of the calcined powder, and the mixing time during the ceramic slurry production. Four types of dielectric green sheets having different values were prepared. About the obtained four types of dielectric green sheets, the amount of contained Zr element was measured using a fluorescent X-ray analyzer, and the amount of this Zr element was converted to ZrO ₂ to the total weight of the dielectric powder. The ratio was the amount of ZrO ₂ . The measurement result of the amount of ZrO ₂ is shown as sheet No. It shows to (Table 1) with S1-S4.

  Subsequently, using the four types of dielectric green sheets, four types of laminates were produced as follows.

  First, apart from the dielectric green sheet, a paste containing nickel as a main component was printed on a polyethylene terephthalate film by a screen printing method and dried to produce a conductor layer pattern to be an internal electrode having a thickness of 1.5 μm.

Next, the dielectric green sheet and the conductor layer pattern serving as the internal electrode are alternately laminated by a plurality of times by thermal transfer so as to have a predetermined positional relationship, and pressed to obtain a laminate block. The laminated body block is cut and separated to produce an individual laminated body. Thus, four types of laminates using the above four types of dielectric green sheets were produced. The four types of laminates produced had the same design specifications except for the dielectric green sheets used, that is, the thickness and number of laminates of the dielectric green sheets, and the area of the conductor layer pattern serving as the internal electrode And the target capacitance was 10 μF _−0% ^{+ 20%} . In addition, the dimensions of the laminate of the individual pieces after cutting were the same so that the outer dimensions of the finished multilayer ceramic capacitor were 1.6 mm in length, 0.8 mm in width, and 0.8 mm in thickness. .

  Next, these four types of laminates were fired to obtain sintered bodies by changing the oxygen concentration in the atmosphere during firing as follows.

First, the laminate was placed in a zirconia-based sheath, treated in an industrial nitrogen gas atmosphere at a maximum temperature of 450 ° C. for 2 hours, and debindered. Thereafter, the binder-treated laminate was treated at a maximum holding temperature of 1200 ° C. for 2 hours in an atmosphere with various oxygen concentrations changed, and fired to obtain a sintered body. The oxygen concentration of the atmosphere at this time was variously changed in the temperature range of the maximum holding temperature of 1200 ° C. and the temperature range of the temperature raising process from 1050 ° C. to 1200 ° C. The oxygen concentration was controlled by the mixing ratio of industrial nitrogen gas, CO ₂ gas, and H ₂ gas, and the oxygen concentration was adjusted by changing the flow rate of H ₂ gas.

  Next, a copper paste is applied to both end faces of the obtained sintered body and baked at 900 ° C. in an industrial nitrogen atmosphere, and then subjected to Ni plating and Sn plating to form external electrodes. Ten types of multilayer ceramic capacitors were produced.

The ten types of multilayer ceramic capacitors produced as described above were evaluated for initial electrical characteristics, reliability, and the presence of internal structural defects in the sintered body. The initial electrical characteristics were evaluated by measuring the electrostatic capacity and dielectric loss tangent (tan δ) at 1 kHz and 1 Vrms, and determining the average value of 100 samples. In addition, the reliability was evaluated for deterioration of insulation resistance after a high-temperature load test in which a DC voltage that is one time the rated voltage was applied continuously at 85 ° C. for 1000 hours for 100 samples. In the case where there is no deterioration of the insulation resistance, the mark is “◯”. As for the internal structure defects of the sintered body, the appearance and the presence or absence of delamination, cracks, etc. of the sintered body were examined by observation of resin embedding. The evaluation results are shown in (Table 1) together with the amount of ZrO ₂ in the dielectric green sheet used for the laminate production and the oxygen concentration log (PO ₂ ) of the atmosphere during firing.

As shown in Table 1, Sample No. Nos. 7 to 10 are multilayer ceramic capacitors produced by the manufacturing method of the reference example in which the oxygen concentration during firing is the same and the oxygen concentration is not adjusted. These multilayer ceramic capacitors are statically controlled by the amount of ZrO ₂ in the dielectric green sheet. In some cases, the capacitance fluctuated and the desired capacitance could not be obtained. Sample No. When the amount of ZrO ₂ becomes too large as in 10, the sintering becomes excessive, and the reliability decreases as the capacitance and dielectric loss tangent increase.

In contrast, sample no. 1 to 6 are monolithic ceramic capacitors produced by the production method according to the embodiment of the present invention, which are produced by performing firing while changing the oxygen concentration according to the amount of ZrO ₂ contained in the dielectric green sheet.

That is, sample no. 1-4, as the atmosphere in the temperature range of the maximum holding temperature of 1200 ° C. during firing, the oxygen concentration is increased when the amount of ZrO ₂ in the dielectric green sheet is large, and the oxygen is increased when the amount of ZrO ₂ is small. The sintered compact was obtained by firing at an oxygen concentration atmosphere as shown in Table 1 with a low concentration. As apparent from the results shown in (Table 1), these sample Nos. In the multilayer ceramic capacitors according to the manufacturing methods of Examples 1 to 4 of the present invention, the influence of the amount of ZrO ₂ in the dielectric green sheet can be reduced, both of which are the target capacitance of 10 μF _−0% ^A capacitance of 10-12 μF within the range of ^{+ 20%} was obtained.

Furthermore, sample no. 5 and 6 are the cases where the atmosphere in the temperature raising process of 1050 ° C. to 1200 ° C. in addition to the temperature range of the maximum holding temperature of 1200 ° C. during firing is large when the amount of ZrO ₂ in the dielectric green sheet is large. Is manufactured by increasing the oxygen concentration and firing in an atmosphere of oxygen concentration as shown in Table 1 to obtain a sintered body. These sample Nos. The multilayer ceramic capacitors according to the manufacturing methods of the embodiments of the present invention of 5 and 6 can further reduce the influence of the amount of ZrO ₂ in the dielectric green sheet, and have a static capacity of 10 to 11 μF which is closer to the target capacitance. An electric capacity was obtained.

  Further, as shown in (Table 1), these sample Nos. The multilayer ceramic capacitors according to the production methods of Examples 1 to 6 of the present invention are reliable without the occurrence of internal structural defects such as delamination and cracks in the sintered body, and without deterioration of insulation resistance in a high temperature load test. It was expensive.

As described above, the method for manufacturing a multilayer ceramic capacitor according to the present invention measures the amount of ZrO ₂ contained in the dielectric green sheet, and changes the oxygen concentration in the atmosphere during firing according to the amount of ZrO _2. As a result, the influence of the amount of ZrO ₂ mixed in the dielectric green sheet can be reduced, and the variation of the dielectric constant of the dielectric layer can be reduced. The target capacitance can be obtained without changing the electrode area. Moreover, there is no occurrence of internal structural defects such as delamination and cracks in the sintered body, and a highly reliable multilayer ceramic capacitor can be manufactured.

In the above embodiment, as dielectric green sheets with different amounts of ZrO ₂ mixed, the raw material powder mixing time and calcining powder grinding time during dielectric powder production, and the mixing time during ceramic slurry production In this example, a dielectric green sheet with different amounts of ZrO ₂ mixed in was consciously produced. However, when the raw material itself such as barium titanate as a main component contains ZrO ₂ and fluctuates, even if the ZrO ₂ content in the dielectric green sheet by variation in the manufacturing process conditions change, and measures the ZrO ₂ content in the dielectric green sheet by elemental analysis equipment such as X-ray fluorescence, the measured quantity A similar effect can be obtained by changing the oxygen concentration during firing according to the above.

  Moreover, in the said embodiment, although it was set as the structure which does not contain a Zr element as a balance composition of dielectric powder, the same effect is acquired even if it contains a Zr element.

In the above embodiment, the maximum holding temperature during firing is 1200 ° C., and the oxygen concentration log (PO ₂ ) in this temperature range is adjusted in the range of −9.24 to −9.75 Pa. Although the proper maximum holding temperature and oxygen concentration differ depending on the composition of the dielectric powder and the amount of ZrO ₂ contained, the maximum holding temperature and oxygen concentration can be adjusted according to the composition of each dielectric powder. preferable. In this case, it is necessary to adjust the oxygen concentration to a concentration within a range in which nickel serving as the internal electrode is not oxidized and the dielectric powder is not reduced.

In the above-described embodiment, an example in which the thickness of the dielectric green sheet is thin, in which the influence of the amount of ZrO ₂ is remarkable, is shown. However, even when the thickness of the dielectric green sheet exceeding 2 μm is thick. Similar effects can be obtained.

The manufacturing method of the multilayer ceramic capacitor according to the present invention can reduce the influence of the amount of ZrO ₂ mixed in the dielectric green sheet, and can reduce the variation of the dielectric constant of the dielectric layer. Since the electric capacity can be obtained, it is particularly useful for manufacturing a high-capacity and high-precision multilayer ceramic capacitor.

Claims (2)

A method for producing a multilayer ceramic capacitor, characterized in that firing is performed by changing the oxygen concentration of the atmosphere during firing according to the amount of ZrO ₂ contained in the dielectric green sheet. The method for producing a multilayer ceramic capacitor according to claim 1, wherein firing is performed while changing the oxygen concentration at least in a temperature range of the maximum holding temperature.